Identify the stars in your night-sky photo, or the craters on the Moon
Plate Solver works out exactly which part of the sky a photo shows, then labels it: constellation figures, named stars and Greek letters, Messier and NGC galaxies, nebulae and star clusters. If the photo records when it was taken, it also marks the Moon and planets; with the place too, the horizon and an altitude/azimuth grid. The result is an interactive sky map: zoom in, tap any star to see what it is, switch layers on and off. Tap a star or galaxy for its distance, size and type, and when the light in your photo left it. A 3D globe shows where the photo sits in the whole sky and, with the time and place, which way the camera pointed and how high. A photo of the Moon gets its seas, craters, mountains and landing sites named instead, at any phase.
More annotated photos in the gallery →
How to use it
- Choose or drop a photo, or paste a link to one (Flickr, Dropbox, Imgur, GitHub or Wikimedia Commons).
- Wait a few seconds while it finds the stars and matches them to a star catalogue.
- Explore, then download the annotated image or share a live link.
Solving lots of images? Get in touch.
What photos work
- Phone night-mode shots and wide-angle Milky Way photos, including trees, hills or buildings in the frame.
- Camera RAW files (NEF, CR2, CR3, ARW, DNG, RAF, ORF, RW2, PEF and more) are decoded on your device too; the decoder (1.4 MB) loads once, only when needed. Phone RAW: Bayer DNGs work, iPhone ProRAW (a linear DNG) is untested.
- Sky quality and star brightness (camera RAW): how dark the sky was, in magnitudes per square arcsecond (as a Sky Quality Meter reads it), with a map of it as a layer, and any star's V magnitude, both measured against the catalogue stars in the same frame. Tap a star, or name it in the panel. A set of RAW photos on the Star trails page gives a star's mean over all of them.
- Fisheye and circular all-sky images. Lens distortion is measured and corrected.
- Telephoto up to about 800 mm on full frame (about 500 mm on APS-C). For these a 1.5 MB catalogue of fainter stars loads once, only when needed.
- The Moon, any phase, as long as the whole Moon is in the photo and at least about 300 px across (roughly 200 mm and up, or a phone at 5–10× zoom). Its seas, craters, mountains, rilles and landing sites are named; tap one for its size and whom it's named after. The Moon maps (0.7 MB) load once, only when needed. Close-ups of part of the Moon aren't supported.
- Not high magnification: telescope close-ups narrower than about 2.5° across don't hold enough catalogue stars. Use nova.astrometry.net for those.
Private, free, works offline
Everything runs in your browser: your photo is never uploaded, and a linked photo is fetched straight from where it's hosted. After the first visit the page works offline, handy at a dark site. Anonymous usage counts are collected; never photos, links or locations (privacy).
Questions
What is plate solving?
Matching the pattern of stars in an image to a star catalogue to find exactly where the camera was pointing, how wide the field is and how it's rotated. Observatories use it to point telescopes; here it runs on your device and also measures the lens.
Why didn't my photo solve?
Usually too few sharp stars: clouds, heavy noise reduction, long star trails, or a field narrower than about 2.5° across. Heavily stretched or composited images can fail too. A frame with more open sky helps; thin cloud over part of it is fine.
Can it measure how bright a star is?
With a camera RAW photo, yes: tap a star, even one with no label (a variable, a nova), or name it under Star brightness, and its card shows its V magnitude with an error, against its catalogue value. The photo is calibrated on the hundreds of catalogue stars in it (Tycho-2), allowing for the atmosphere and the lens; one 10-second photo at 14 mm gives about ±0.06–0.10 mag for stars of V 6–8, and a set of photos on the Star trails page about ±0.03. A cloudy photo, or a star that's saturated, has a close neighbour or sits on the foreground, is refused with the reason. JPEG isn't offered: the camera's tone curve leaves it at about ±0.12.
Can it identify the craters on the Moon?
Yes. Drop a photo showing the whole Moon, at any phase, about 300 px across or more, and it matches the Moon's terrain against NASA maps lit the way the Sun lit it that night. It names the seas, craters, mountains, rilles and landing sites (including Apollo and Chandrayaan-3); tap any of them for its size and whom it's named after. The original photo from the camera or phone solves fastest: screenshots and edited copies lose the capture time, so they take longer.
Why are the Moon or planets missing?
They need the capture time. The Moon moves its own width every hour, so it's shown only when the time zone is known (from the camera, GPS, or entered under Time & place) or the photo shows it where expected. An edited copy often loses the original capture time.
Can I share the result?
Yes. Put the photo online (Flickr, Dropbox, Imgur, GitHub, Wikimedia Commons) and use Share: the link opens the photo with all labels on any device, and the photo stays wherever you host it. Google Photos and Google Drive links can't be opened by other sites. Exported images carry their sky coordinates, so planetarium software such as WorldWide Telescope can place them on the sky.
Can I send photos to it from my phone's gallery?
On Android, yes: in Chrome, choose Install app (or Add to Home screen) from the menu. Plate Solver then appears when you share a photo from Google Photos, your gallery or a chat app. The photo is handed to the app on your phone and is never uploaded. On iPhone, open the site and use Choose a photo.